It has become evident in the last several years that the mutation rate is under genetic control. In bacteria and yeast the frequency of induced mutations can be either increased or decreased by blocking one or another pathway of DNA repair. This project is designed to determine the relationship between DNA repair and mutagenesis in Drosophila melanogaster. Two approaches are being taken: (1) Mutagen-sensitive mutants have been isolated and characterized as to their effects on DNA repair and are being tested for effects on mutation frequency; and (2) mutants which increase the spontaneous mutation frequency (mutators) will be isolated and characterized.